Interferon gamma inhibits growth of human pancreatic carcinoma cells via caspase-1 dependent induction of apoptosis.

BACKGROUND AND AIMS: The poor prognosis of pancreatic cancer is partly due to resistance to a broad spectrum of apoptotic stimuli. To identify intact proapoptotic pathways of potential clinical relevance, we characterised the effects of interferon gamma (IFN-gamma) on growth and survival in human pancreatic cancer cells. METHODS: IFN-gamma receptor expression and signal transduction were examined by reverse transcriptase-polymerase chain reaction (RT-PCR), immunoprecipitation, western blot analysis, and transactivation assays. Effects on cell growth and survival were evaluated in terms of cell numbers, colony formation, cell cycle analysis, DNA fragmentation, and poly(ADP ribose) polymerase (PARP) cleavage. RESULTS: All four pancreatic cancer cell lines examined expressed functional IFN-gamma receptors and downstream effectors, including the putative tumour suppressor interferon regulatory factor 1 (IRF-1). IFN-gamma treatment profoundly inhibited anchorage dependent and independent growth of pancreatic cancer cells. Cell cycle analyses revealed subdiploid cells suggesting apoptosis, which was confirmed by demonstration of DNA fragmentation and PARP cleavage. Time and dose dependency of apoptosis induction and growth inhibition correlated closely, identifying apoptosis as the main, if not exclusive, mechanism responsible for growth inhibition. Apoptosis was preceded by upregulation of procaspase-1 and accompanied by proteolytic activation. Furthermore, the caspase inhibitor z-vad-fmk completely prevented IFN-gamma mediated apoptosis. CONCLUSIONS: These results identify an intact proapoptotic pathway in pancreatic cancer cells and suggest that IRF-1 and/or procaspase-1 may represent potential therapeutic targets to be further explored.

Molecular mechanism of interferon alfa-mediated growth inhibition in human neuroendocrine tumor cells.

BACKGROUND & AIMS: Although human neuroendocrine tumors respond to interferon (IFN)-alpha treatment in vivo, the underlying mechanisms of growth inhibition are poorly understood. To characterize the antiproliferative effects at a molecular level, we explored the growth-regulatory action of IFN-alpha in the human neuroendocrine tumor cell lines BON and QGP1. METHODS: IFN-alpha receptor expression and signal transduction were examined by reverse-transcription polymerase chain reaction, immunoblotting, subcellular fractionation, and transactivation assays. Growth regulation was evaluated by cell numbers, soft agar assays, and cell cycle analysis using flow cytometry. Expression and activity of cell cycle-regulatory molecules were determined by immunoblotting and histone H1-kinase assays. RESULTS: Both cell lines expressed IFN-alpha receptor mRNA transcripts. Ligand binding initiated phosphorylation of Jak kinases and Stat transcription factors, resulting in Stat activation, nuclear translocation, and transcription from an ISRE-reporter construct. Prolonged IFN-alpha treatment dose-dependently inhibited both anchorage-dependent and -independent growth. Cell cycle analysis of IFN-alpha-treated, unsynchronized cultures revealed an increased S-phase population, which was further substantiated in G(1) synchronized QGP1 cells. IFN-alpha-treated cells entered S phase in parallel to control cultures, but their progress into G(2)/M phase was delayed. Both cellular cyclin B levels and CDC 2 activity were substantially reduced. The extent and time course of this reduction corresponded to the observed S-phase accumulation. CONCLUSIONS: IFN-alpha directly inhibits growth of human neuroendocrine tumor cells by specifically delaying progression through S phase and into G(2)/M. These cell cycle changes are associated with inhibition of cyclin B expression, resulting in reduced CDC2 activity.